Optoelectronics is a rapidly expanding technology that plays an increasingly important role in many aspects of modern society (e.g., communication over optical fibers, computer storage and displays, etc.). With the increasing number of actual and potential commercial applications for optoelectronic systems, there is a need to develop cost effective and precise manufacturing techniques for assembling optoelectronic modules (e.g., fiber-optic cable repeaters, transmitters, receivers, etc.).
One of the problems associated with developing such cost effective manufacturing techniques is the high precision required to align components (e.g., lasers, photodiodes, optical fibers, etc.) to assure proper optical coupling and durability. Typically, an optoelectronic module includes a package or housing containing an optoelectronic device (e.g., semiconductor laser, light emitting diode, photodiode, etc.) coupled to an optical fiber (e.g., single mode, multimode or polarization maintaining) that extends from the package. A major challenge in assembling such optoelectronic modules is in maintaining optimal alignment of the optoelectronic device with the optical fiber to maximize the optical coupling. In order to obtain maximum optical coupling, it is typically desired that the core-center of the optical fiber be precisely aligned with that of the optoelectronic device. In some cases, such as with a single-mode optical fiber, the alignment between the optoelectronic device (e.g., a laser) and the optical fiber must be within tolerances of 1 μm or less.
A conventional method for aligning an optoelectronic laser with an optical fiber is known as “active alignment,” where the laser is bonded to a substrate and one end of a desired type of optical fiber is positioned in close proximity to a light-emitting surface of the laser in order to transmit light emitted from the laser through the optical fiber. A photodetector, such as a large area photodetector, is positioned at the opposing end of the fiber to collect and detect the amount of light (optical radiation) coupled to and transmitted through the fiber. The position of the fiber is incrementally adjusted relative to the laser either manually or using a machine until the light transmitted through the fiber reaches a maximum, at which time, the optical fiber is permanently bonded to the same substrate that the laser was previously bonded to.
An optoelectronic photodiode, such as a PIN or APD photodiode, may similarly be coupled to an optical fiber through “active alignment” by bonding the photodiode to a substrate and positioning the end of the optical fiber that is to be coupled to the photodiode in proximity to the light receiving surface of the photodiode. Light is then radiated through the opposing end of the optical fiber using a light source and the position of the fiber is incrementally adjusted relative the photodiode until the photodiode's electrical response reaches a maximum, wherein the optical fiber is then bonded to the substrate supporting the photodiode.
Alternatively, such “active alignment” of an optoelectronic device (e.g., laser or photodiode) to an optical fiber has been attempted by initially bonding the optical fiber to the substrate, moving the optoelectronic device into alignment by detecting the maximum optical radiation through the fiber, and then bonding the aligned optoelectronic device to the substrate supporting the fiber. However, either alignment process is labor intensive and very time consuming and, therefore, very expensive.
More recently, a new optoelectronic device bonding technique known as “self-alignment” based upon solder bump flip-chip technology has been employed to reduce die bonding accuracies from tens of micrometers toward a few micrometers. In this “self-alignment” process, small (approximately 75 μm diameter) solder bumps are placed around the periphery of the optoelectronic device. These solder bumps serve to “self-align” the device (e.g., through surface tension) as the solder is heated to a molten state and during reflow of the solder.
When coupling light between optical fibers or waveguides and optoelectronic devices, the self-alignment process eliminates the need for actively adjusting the position of the device relative to the fiber or waveguide when the solder is molten. This self-alignment process, however, has only been successfully used to assemble optoelectronic modules where the optical/mechanical tolerances are fairly loose (e.g., approximately 10 μm) and has not yet been shown to be production-worthy in single mode optoelectronic circuits where a few micrometer bonding accuracy is considered too coarse, leaving the highly labor-intensive and time-consuming active alignment method as the only production-worthy alternative.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object the present invention to provide new and improved alignment apparatus and methods for optical components in an optical subassembly.
Another object of the present invention is to provide new and improved alignment apparatus and methods for optical components that require less labor and time in the manufacture of optical subassemblies.
Another object of the present invention is to provide new and improved alignment apparatus and methods for optical components that improve the fabrication efficiency and manufacturing capabilities of optoelectronic modules and packages.
Another object of the present invention is to provide new and improved alignment apparatus and methods for optical components that stabilize the alignment over wide temperature variations.